Most user equipment (UE) handsets support two different radio access technologies. One such radio access technology is wide local area network (WLAN). Another such radio access technology is cellular radio technology defined by the third generation partnership project (3GPP), and in particular, universal terrestrial radio access network (UTRAN) or evolved-UTRAN (E-UTRAN). Some UEs can route Internet protocol (IP) traffic over a single radio access interface at a time, while other UEs can route IP traffic over two different radio access interfaces at a time. In both cases, a network operator desires to control which radio access technology is selected and which traffic is routed over one radio access technology as opposed to another.
Many operators have adopted a simple offloading strategy. The basic principle of this strategy is that, whenever a WLAN access point is available and visible to a UE, some or all of the traffic is routed to the WLAN, thereby offloading the 3GPP radio access network. This is known as WLAN offload and provides rudimentary traffic load balancing among different access networks.
WLAN offload has many benefits, but also has many challenges. Desirably, a single subscriber should only have to login once to access both networks. Also, there should be seamless mobility between access networks. Another problem to be solved is the optimization of the user experience regardless of the access network and the effective usage of the radio and backhaul resources. WLAN access points can be highly utilized and/or deployed with lower backhaul capacity to enable cost efficient network deployments. In some cases, the end user experiences degrade if the UE routes all or some of its IP traffic over the WLAN.
Each radio access technology has its own protocol, policies and procedures which may be referred to as radio admission control (RAC). Radio admission control is responsible for radio bearer traffic admission control and traffic scheduling. In long term evolution (LTE) networks, the radio resources are managed by distributed radio access nodes such as eNodeBs (eNBs). In wideband code division multiple access (WCDMA) networks, the radio resources are managed by distributed radio access nodes such as nodeBs (NBs) and radio network controllers (RNCs). In WLAN networks, the radio resources are managed by distributed radio access nodes like the access points (APs) and access controllers (ACs). The backhaul resources are managed by another set of protocols, policies and procedures often referred to as Ethernet and IP traffic management. The backhaul resources are managed by nodes such as routers and switches and can be remotely monitored by radio access node sites such as the NodeBs, APs and ACs.
An access network and selection function (ANDSF) specified by 3GPP is used to manage inter-systems mobility policy (ISMP), inter-system routing policy (ISRP) and access network discovery information (ANDI). The ANDSF is located in the operator's IP network and supports the open mobile alliance device management (OMA-DM) protocol. The ANDSF may initiate the provision of information from the ANDSF to the UE in a push mode of operation. The UE may also initiate the provision of all available information from the ANDSF in a pull mode of operation. The ISMP, ISRP and ANDI can also be statically preconfigured by the operator on the UE. The ISMP, ISRP and ANDI may be provided to the UE by the ANDSF via an S14 interface and may take precedence over the policies and information preconfigured on the UE.
The ISMP is a set of operator-defined rules and preferences that affect the inter-system mobility decisions taken by the UE when it can route traffic over a single radio interface. A purpose of the ISMP is to select the preferable access technology that should be used by the UE to access all destinations. The granularity of access system connectivity is per packet data network (PDN) connection basis. This implies that when a handover occurs, all of the IP flows belonging to the same/single PDN connection are moved from the source access system to the target access system.
The ISRP is a set of operator-defined rules and preferences that affect the inter-system routing decisions taken by the UE when it can route traffic simultaneously over multiple radio interfaces. A purpose of the ISRP is to select the preferable access technology that should be used by the UE to access a specific access point name (APN) or a specific IP flow. The granularity of access system connectivity is per IP flow or per APN basis. This implies that when a handover occurs, some IP flows of the PDN connection are routed via one access system while simultaneously, some IP flows of the same PDN connection are routed via another access system. The other possibility is that some PDN connections are routed via one access system while simultaneously some PDN connections are routed via another access system.
The ANDI provides further information for the UE to access the radio access network defined in the ISMP or in the ISRP. Upon UE request, the ANDSF may provide a list of access networks available in the vicinity of the UE.
A problem with the ISMP, ISRP and ANDI policies is that they provide a preferential list of access technologies that a UE should use in a given location and/or at a given time of day and such list of preferences is static or semi-static. In today's network, where certain radio access networks are always busy or when resource consumption highly fluctuates, planning a successful time of day to offload UEs or certain IP flows while achieving optimal subscriber performance delivery and optimal use of the available cell and backhaul transport resources is a very difficult task and may not even be possible.
It is possible to introduce a bandwidth broker server within each radio access network. The broker is responsible for collecting and correlating the load status on the cells across radio access networks and to accept/deny each subscriber connection request when a cell or transport path across the transport network is congested. This method has limitations. It requires additional servers to deploy and manage in each radio access network; potentially one set of servers per radio access technology (WLAN, E-UTRAN, UTRAN and Global System Mobile Edge Radio Access Network (GERAN)). It also requires continuous transfer of cell and path performance information to a centralized server. Fundamental changes to the signaling architecture would be required when a bandwidth broker is introduced. Introduction of the bandwidth broker would require a new bandwidth broker client or radio network server. This adds significant delay during admission control and handover decisions.